The outcome of infection is determined not only by the virulence of an infecting organism, nor by the microbial burden, nor by the intensity of the innate immune response, but by the ability of the host to accommodate itself to each of these factors. Homeostatic mechanisms normally limit the intensity of an inflammatory response, maintain cardiovascular stability, and bring about the repair of damaged tissues, concurrent with the initiation of the immune response itself. We have previously identified mutations that diminish the ability of the host to survive infection, including a mutation in Kcnj8, a component of an ATP-sensitive potassium channel of the vascular endothelium. Without this channel, mice suffer myocardial infarction and cardiovascular collapse during infection with mouse cytomegalovirus, or after injection of minute quantities of lipopolysaccharide. Many other mechanisms maintain homeostasis during infection, and using a forward genetic screen for hypersensitivity to DSS-induced colitis, we have identified several of them. Mutations that limit proliferation of epithelial cells, diminish the ability to sense microbes, prevent secretion or intracellular migration of vesicles, impair the unfolded protein response, or the systemic glucocorticoid response all permit severe colitis to develop following minor septic injury to the mucosa. Some of these mutations (e.g., mutations affecting Toll-like receptors, signaling proteins downstream, and the glucocorticoid response) are of very broad importance in surviving infection, operating in many different infectious disease states. We propose to identify many more such mutations and establish a strong mechanistic model of the critical homeostatic mechanisms that allow the host to recover from a defined stress on the enteric mucosa. We will further determine whether these mutations have broad effects on susceptibility to infection, and whether they might be combined to create synthetic phenotypes that affect the course of infection.